1. Field of the Invention
The invention relates to a color wheel, more particularly to a reflective color wheel that is capable of reducing losses in light energy to improve light utilization.
2. Description of the Related Art
As shown in FIG. 1, a conventional optical projecting system includes a light source 1, a light tunnel 2, a transmissive color wheel 3, a digital micro-mirror device (DMD) 4, and a screen 5. The light source 1 is capable of generating source light 101. The light tunnel 2 is capable of receiving, guiding, and focusing the source light 101 to result in focused light. The transmissive color wheel 3 is rotatable about a rotation axis (X1), and includes a plurality of spiral light-filtering components 301 that are distributed around the rotation axis (X1). The light-filtering components 301 of the transmissive color wheel 3 include sequentially arranged red, blue and green light-filtering components (r), (b), (g), as illustrated in FIG. 2. The red, blue and green light-filtering components (r), (b), (g) allow transmission of red, blue and green light therethrough, respectively. The transmissive color wheel 3 rotates at an extremely high speed about the rotation axis (X1) as the focused light exits the light tunnel 2 so as to filter the focused light into red, blue, and green focused light components sequentially and cyclically. The red, blue, and green focused light components are subsequently projected toward the DMD 4, which modulates the red, blue, and green focused light components into red, blue and green modulated light components, respectively, and projects them onto the screen 5 so that colored images are presented on the screen 5.
Although by utilizing the transmissive color wheel 3, the conventional optical projecting system is capable of projecting colored images, the following shortcomings exist during use:
1. As shown in FIG. 2, when the focused light passes through the red light-filtering component (r), only the red focused light component thereof is transmitted toward the DMD 4, while the blue and green focused light components are reflected back to the light tunnel 2. Similarly, when the focused light passes through the blue light-filtering component (b), only the blue focused light component thereof is transmitted toward the DMD 4, while the red and green focused light components are reflected back to the light tunnel 2. When the focused light passes through the green light-filtering component (g), only the green focused light component thereof is transmitted toward the DMD 4, while the red and blue focused light components are reflected back to the light tunnel 2. This results in high losses in light energy, i.e., reduction in light utilization, in addition to presenting adverse effects on brightness of projected images.
2. As shown in FIG. 3, another transmissive color wheel 6 is used instead of the transmissive color wheel 3 in a modified conventional optical projecting system. The transmissive color wheel 6 includes three fan-shaped light-filtering components 602, which include red, blue and green light-filtering components (r′), (b′), (g′) that allow transmission of red, blue and green light therethrough, respectively. Therefore, as with the red, blue and green light-filtering components (r), (b), (g) of the transmissive color wheel 3, the red, blue and green light-filtering components (r′), (b′), (g′) of the transmissive color wheel 6 only allow corresponding colors of the focused source light 101 to be transmitted therethrough, with a major portion of the focused source light 101 reflected back to the light tunnel 2 (as shown in FIG. 1).